1. Field of the Invention
The present invention relates to pneumatic operation of sliding doors in general, and in particular to apparatus for pneumatic operation of the sliding door assemblies used on transport containers, such as trailers or other vehicles.
2. Background
The use of trucks, tractor-trailers, railroad cars, etc. for transporting palletized or containerized materials and bulk particulate commodities is well known. The hauling boxes or transport containers used to hold the materials typically require movable gates or doors allowing for the ingress and egress of the material through discharge openings.
In the typical flat-bottom trailer, it is well known to provide doors that are vertically oriented in the closed position and that slide upward to an open position. For instance, a sectional-type sliding door for trucks or trailers may include a series of similar horizontal panels connected by hinges that allows pivoting between the panels. It is common to use such sectional-type doors at the rear end openings of trucks or trailers. Typically, the sides of the panels, or the hinge means between the panels, have rollers which run in vertical tracks at the sides of the opening and horizontal legs above the rear of the opening. In the typical flat-bottom trailer, these doors are opened and closed manually. Manual operated doors expose the operator to potential injuries. Moreover, manual operated doors are not amenable to partial opening in order to restrict flow of particulate matter through the discharge opening.
Similar to the section-type doors are sheet doors. Sheet doors have flexible door panels that, typically, are guided around rollers between the open and closed positions. Other known sliding doors include roller doors, which are made of multiple, relatively thin, horizontal slats. Rotation of a drum or roller located at the top of the door causes the roller door to wrap around (or unwrap from) the drum, thus opening (or closing) the door.
Flat-bottomed or hopper-type trailers capable of self-unloading bulk particulate and/or chunk material via a conveyor mechanism and having slidable gates for providing a variable size discharge opening during an initial opening stage are also known. Known mechanisms for sliding and/or pivoting the gate, or only a portion of the gate, include hydraulic or pneumatic cylinders, cables attached to an electric winch or drum, or manual operation. In some instances, further opening the gate allows it to pivot, thereby providing an unrestricted discharge opening for unloading the contents from the box.
It is also known to provide movable gates for controlling the amount of particulate matter being discharged from pivoting or tilt-type transport containers, i.e., dump truck-type beds. Typically, the rear walls of such dump truck-type beds are fashioned as gates that pivot around pins located at the top of the rear wall. One known design for a tilt bed incorporates a rear wall having a movable gate that both slides and pivots. A pair of hydraulic rams, located on either side of the gate, slides the gate upward until a select height is reached, whereupon the gate may pivot completely open. In another known design, a lower portion of a pivotable gate is independently pivotable via hydraulic cylinders and a linkage mechanism.
Typically, piston/cylinder mechanisms, whether hydraulic or pneumatic, are bulky and heavy and, unlike motors, are not amenable to being retrofit. Further, all hydraulic drive mechanisms are not environmentally friendly, operating with potentially harmful hydraulic fluids. Even further, pressurized supplies of hydraulic fluid for operating the hydraulic cylinders are typically not transported with the transport container.
What is needed is an apparatus that is relatively lightweight, small, and environmentally friendly. Moreover, with respect to tractor-trailers, what is needed is an apparatus that is powered from existing pneumatic systems carried by the tractor. Additionally, there is a need to retrofit existing transport containers constructed with hydraulic or electric motors for raising or lowering sliding doors with pneumatically powered sliding door systems, where such retrofit is conducted with minimal reconstruction or replacement of the components of the existing conveyor systems.